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Topic: Technology [alternatives to traditional roof a/c units] (Read 1162 times) previous topic - next topic

Re: Technology

Reply #25 –
That's looking like a pretty complex installation.  I think you could quite simply install one of the ceiling mount evaporator units (the ones that are made to retrofit to a ducted  conventional split system ac) in the cabinet above bed.  Extend duct as per Foretravel on into the living room.  Leave condensing unit in case, remove useless dash air condenser, build insulated enclosure in space, add grille, slide in standard condensing unit. Still not trivial but would allow you to easily replace any part of system without having to make custom mods.  The output of a 24K btu unit will vastly exceed two roofmount 15K units and provide real heat if desired. 
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: Technology

Reply #26 –
Quote from: Chuck Pearson –
That's looking like a pretty complex installation.  I think you could quite simply install one of the ceiling mount evaporator units (the ones that are made to retrofit to a ducted  conventional split system ac) in the cabinet above bed.  Extend duct as per Foretravel on into the living room.  Leave condensing unit in case, remove useless dash air condenser, build insulated enclosure in space, add grille, slide in standard condensing unit. Still not trivial but would allow you to easily replace any part of system without having to make custom mods.  The output of a 24K btu unit will vastly exceed two roofmount 15K units and provide real heat if desired. 
You would still need 240 volts for the 24K unit. How does a 24k unit outperform two 15k btu rooftop units? In air conditioning, BTU's are the amount of heat removed. Does not matter how the unit operates, removing one btu is removing one btu. Foretravels are well insulated but pushing cold air  through a duct down 40 ft of coach 2 inches under a hot roof would not be very efficient, to say nothing about the size and noise of the blower required.
Not trying to throw cold water on your idea's, but the 2 million dollar coach makers, where money is no object, have tried every method and are now going back to good old roof airs.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: Technology [alternatives to traditional roof a/c units]

Reply #27 –
While I agree our dash air is weak compared to the later units we came through Nevada this week then through the baker grade to so cal.

Outside on the world tallest thermometer it was 104 and with the dash air on high and the front roof air on at 75 and auto fan on the front was comfortable.  Small fan clipped to the passenger side window frame helped the sun side.

Like I said.  Comfortable. 
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Technology [alternatives to traditional roof a/c units]

Reply #28 –
I am very happy with my present dash air. Have never had a diesel pusher that had a good engine driven compressor dash air, almost always had to supplement with a roof air and run generator. Present coach dash air will actually keep front area of coach cool in 95 f. ambient temps. Am seeing about about a 38 degree drop through the evaporator with blower on high. I think Mel at MOT told me once that if he had $5 for every coach he sold with a non working dash ac, he would be a rich man. Of course, I have no idea how many thousands of dollars the PO spent on getting it working right.
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: Technology [alternatives to traditional roof a/c units]

Reply #29 –
Quote from: jcus –
How does a 24k unit outperform two 15k btu rooftop units?

It happens when the 24k BTU unit actually removes 24K BTU, and the two so called 15K BTU units  actually remove around 9K each. 


"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: Technology [alternatives to traditional roof a/c units]

Reply #30 –
Inverter compressors can and do go into overdrive at 80hz vs 60 hz for a limited amount of time, or till they max out the rated amperage. Control boards are very smart. A 12k btuh unit may actually have an 18k btuh compressor that the control board that allows to work as hard as needed, and modulate evaporator fan & condenser fans to provide the biggest bang for the buck
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake

Re: Technology [alternatives to traditional roof a/c units]

Reply #31 –
Quote from: Chuck Pearson –
It happens when the 24k BTU unit actually removes 24K BTU, and the two so called 15K BTU units  actually remove around 9K each. 



Any documentation on why you think a 15k unit only removes 9k BTU?
Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: Technology [alternatives to traditional roof a/c units]

Reply #32 –
Quote from: jcus –
Quote from: Chuck Pearson –
It happens when the 24k BTU unit actually removes 24K BTU, and the two so called 15K BTU units  actually remove around 9K each. 



Any documentation on why you think a 15k unit only removes 9k BTU?
Now that the cooling question has entered the conversation, I have wondered why my 2 13k units which would be over 2 tons cooling on a residential rating don't cool the coach as good as my one 1 1/2 ton (18k) that I have in a room with more cu. ft. than the coach. I have guessed that the distribution was the cause. But are these coach units being over rated? The room has west facing 8' window and does have air space in the attic which I figured cancelled each other out..
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Technology [alternatives to traditional roof a/c units]

Reply #33 –
https://www.energydepot.com/RPUcom/library/BUILD001.asp

Even dual pane windows do not have very much insulating quality especially when compared to sheetrock, plywood, fiberglass insulation etc. and your coach has a lot of windows.  Your house ceiling may have up to r-32 insulation valve, The foam in the roof of a Foretravel may be as low as r-10. I have closed cell blinds on every window on my coach, If  I Ieave them open, I will need both roof airs, if I close them all, one ac will keep the coach cool.
Simple experiment, cool coach to 75 f. shut off ac and leave. Come back in 2 hours and take temps inside. Do the same thing in your room in your house and compare results.


Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.

Re: Technology [alternatives to traditional roof a/c units]

Reply #34 –
Quote from: jcus –
Any documentation on why you think a 15k unit only removes 9k BTU?

No, observation and comparison only.  It's a reasonable guess that rooftop units are not producing the optimistic 15K BTU they were rated at.  In lab conditions.  Possibly with voltage tuned to optimum.  New. 

These splits, or at least the ones I've had experience are hitting way above their numbers.  I've replaced a two ton older conventional with a 12K and the performance is far superior, cooling wise.  Using a fraction of the power. 
"Not so  long ago we were a nation of risk takers, riding five million pounds of  thrust straight into space."  Joe Gresh
Chuck Pearson
1996 U295
2018 Can Am X3 TurboRS

Re: Technology [alternatives to traditional roof a/c units]

Reply #35 –
Split units are used all over Asia and in many places in Europe and in many cases are far more efficient and cool better than window or central units in many applications.
The problem is the application.  With a 12 by 12 room with few windows and no heat sources and fairly good insulation. a small split unit evaporator unit near the ceiling will do a great job.
Now take a 40 by 10  box moving over a 120 degree surface with a 100000 btu heat source on one end a 20000 btu heat source on the other, with lots of  big windows and direct sun on at least on the roof and probably on one side as well. Add in many small barely noticeable air leaks, and maybe r-6 insulation overall, and only be able to use ac compressors that run on only 120 volts,  and you will see why motorhome ac's seem so inefficient.

Jim C.
coachfree, previous 1997, 1999, 2000, and 2003 Foretravels.
 

Re: Technology [alternatives to traditional roof a/c units]

Reply #36 –
Quote from: Chuck Pearson –
These splits, or at least the ones I've had experience are hitting way above their numbers.  I've replaced a two ton older conventional with a 12K and the performance is far superior, cooling wise.  Using a fraction of the power. 

I would agree that the current RV rooftops are not delivering into the coach what they claim. My Coleman units has an unsealed shaft leaking air on the evaporator side. Furthermore I think the motors may be running in reverse on both units.
 Certain 120 v single phase motors can and do operate backwards. My units draw air  through the condenser coil on the vacuum void side (rear facing) of a moving vehicle and discharge the 140 degree air only to be sucked back thru the condenser coil.
Oriental splits can post some extremley high efficiency numbers since ARI has not been able how to test them apples to apples.
Old Phart Phred, EIEIO
89 GV ored 36' #3405 300 hp cat 3208 ATAAC side radiator, mountain tamer exhaust brake